Electronic transport through rubrene single-crystal field-effect transistors (FETs) is investigated experimentally in the high carrier density regime (n~0.1 carrier molecule−1). In this regime, we ...find that the current does not increase linearly with the density of charge carriers, and tends to saturate. At the same time, the activation energy for transport unexpectedly increases with increasing n. We perform a theoretical analysis in terms of a well-defined microscopic model for interacting Fröhlich polarons, which quantitatively accounts for our experimental observations. This work is particularly significant for our understanding of electronic transport through organic FETs.
The interplay of Coulomb repulsion and geometrical frustration on charge-driven quantum phase transitions is explored. The ground-state phase diagram of an extended Hubbard model on an anisotropic ...triangular lattice relevant to quarter-filled layered organic materials contains homogeneous metal, "pinball," and threefold charge ordered metallic phases. The stability of the pinball phase occurring for strong Coulomb repulsions is found to be strongly influenced by geometrical frustration. A comparison with a spinless model reproduces the transition from the homogeneous-metallic phase to a pinball liquid, which indicates that the spin correlations should play a much smaller role than the charge correlations in the metallic phase close to the charge-ordering transition. Spin degeneracy is, however, essential to describe the dependence of the system on geometrical frustration. Based on finite-temperature Lanczos diagonalization we find that the effective Fermi temperature scale T* of the homogeneous metal vanishes at the quantum phase transition to the ordered metallic phase driven by the Coulomb repulsion. Above this temperature scale "bad" metallic behavior is found which is robust against geometrical frustration in general. Quantum critical phenomena are not found whenever nesting of the Fermi surface is strong, possibly indicating a first-order transition instead. "Reentrant" behavior in the phase diagram is encountered whenever the 2kF charge-density wave instability competes with the Coulomb driven threefold charge order transition. The relevance of our results to the family of quarter-filled materials, θ-(BEDT-TTF)2X, is discussed.
Grapsoid and ocypodoid crabs receive a lot of attention in the literature due to their predominance and important role as primary and secondary consumers in intertidal as well as supratidal marine ...habitats. They are especially species‐rich in the tropics, where they have been found to repeatedly invade terrestrial and freshwater habitats. However, the systematics of the crabs belonging to these two superfamilies is still not settled, despite recent steps clarifying phylogenetic relationships and introducing new taxa. In this study, a molecular phylogeny of grapsoid crabs primarily based on East African representatives is constructed based on DNA sequences of the mitochondrial small and large ribosomal subunits (12S and 16S rRNA), thus complementing previous molecular taxonomic studies that had been carried out with the American and East Asian fauna. In addition, selected representatives of all ocypodoid families and subfamilies were included. The monophyly of Grapsidae, Ocypodidae (sensu stuctu), Sesarmidae and Varunidae is well confirmed, if the genera Cyclograpsus, Helice are considered Varunidae and Euchirograpsus a Plagusiidae, as previously suggested. The monophyly of the family Gecarcinidae cannot be supported with our data. The family Plagusiidae in its present composition is polyphyletic. Special attention was given to the large family Sesarmidae, which has many endemic genera in the Indo‐West Pacific. According to this study, two of the most speciose genera, Chiromantes and Parasesarma, are not monophyletic and need to be redefined. On the higher taxonomic level, it becomes evident that both superfamilies, Grapsoidea and Ocypodoidea, are not monophyletic in their current composition, as exemplified by a proposed sister group relationship of Varunidae and Macrophthalmidae. These results confirm those from previous molecular studies and we therefore propose to refrain from the traditional use of the Grapsoidea and Ocypodoidea as monophyletic superfamilies and treat the constituent families separately.
Riassunto
I granchi appartenenti alle superfamiglie Grapsoidea e Ocypodoidea da sempre sono oggetto di notevole interesse scientifico a causa del loro importante ruolo ecologico negli ambienti intertidali o sopratidali. Le due superfamiglie sono particolarmente rappresentate, in termini di numero di specie e d'abbondanza relativa, nelle zone tropicali e subtropicali, dove hanno invaso ripetutamente anche ambienti dulcacquicoli e terrestri. La sistematica delle specie appartenenti a queste due superfamiglie è ancora lontana dall'essere completamente risolta, nonostante studi molecolari recenti abbiano chiarito specifiche relazioni filogenetiche e definito nuovi taxa. Questo studio ha ricostruito la filogenesi di alcune specie di Grapsoidea dell'Africa Orientale sequenziando una porzione delle due subunità ribosomali del DNA mitocondriale (12S e 16S rRNA), confermando e completando precedenti studi molecolari condotti su specie americane e asiatiche. In questo studio sono stati inclusi anche rappresentanti di tutte le famiglie e sottofamiglie di ocipodidi. I nostri risultati confermano la monofilia della famiglia Grapsidae, Ocypodidae (sensu stuctu) Sesarmidae e Varunidae a condizione che, secondo quanto recentemente suggerito, i generi Cyclograpsus e Helice siano rimossi dalla famiglia Sesarmidae ed attribuiti ai Varunidae, ed Euchirograpsus dalla famiglia Varunidae ai Plagusiidae. Invece, i nostri dati supportano solo debolmente o non supportano per niente la monofilia della famiglia Gecarcinidae. La famiglia Plagusiidae è probabilmente polifiletica. Questo studio pone inoltre particolare attenzione alle relazioni interne alla famiglia Sesarmidae che include molti generi endemici nell'area Indo‐Pacifica occidentale. Sulla base dei nostri dati, i generi Chiromantes, Parasesarma e Perisesarma sono polifiletici e necessitano di essere ridefiniti. Infine, i risultati di questo studio mostrano chiaramente che la superfamiglia Grapsoidea e Ocypodidea non sono monofiletiche così come attualmente definite, come evidenziato dalla relazione di sister group tra Varunidae e Macropthalmidae. Questo conferma i risultati di precedenti studi molecolari e pertanto proponiamo di non attenersi al tradizionale uso delle superfamiglie Grapsoidea ed Ocypodoidea.
A nucleotide sequence analysis of a portion of the mitochondrial large ribosomal subunit was performed to define the phylogeography of the threatened crayfish Austropotamobius (Decapoda; Astacidae) ...in Italy. We collected 61 specimens from 31 localities across the Italian peninsula. For the phylogenetic inference, we combined the 61 Austropotamobius spp sequences obtained from this study with 18 sequences deposited in GenBank and corresponding to Italian, French, Irish, Swiss, and Slovenian locations. Among the analysed sequences, 34 distinct haplotypes were detected. Our results confirmed the presence of both A. pallipes and A. italicus in the Italian peninsula and the existence within the latter species of a strong intraspecific genetic variation, due to the occurrence of four subspecies with a well-defined geographic distribution. From a conservation viewpoint, Italy, with its high haplotype variability, may be considered a 'hot spot' for the genetic diversity of the European native crayfish Austropotamobius. We suggest that re-introduction programs should be conducted with extreme caution in Italy, since not only the two Austropotamobius species but also the four A. italicus subspecies are genetically and taxonomically separate units and require independent conservation plans.
Purpose
The purpose of this study was to compare two types of posterior-stabilized (PS) mobile-bearing (MB) total knee arthroplasties (TKAs). The hypothesis was that no major differences were going ...to be found among the two TKA designs.
Methods
Two cohorts of patients who were divided according to implant design (Cohort A, new design gradually reducing radius PS MB TKA; Cohort B, traditional dual-radius PS MB TKA) were analyzed by means of intraoperative navigation. All operations were guided by a non-image-based navigation system that recorded relative femoral and tibial positions in native and implanted knees during the following kinematic tests: passive range of motion (PROM), varus–valgus stress test at 0° and 30° (VV0, VV30) and anterior/posterior drawer test at 90° of flexion (AP90).
Results
There were no significative differences in kinematic tests between the two implants. Cohort A, however, showed a different post-implant trend for VV0 and VV30 that were lower than the pre-implant ones, as expected, while for Cohort B, the trend is opposite. However, the gradually reducing radius prosthesis (Cohort A) showed a trend of improving stability (29% compared to the preoperative status) in mid-flexion (VV30) which the traditional dual-radius design (Cohort B) would not. Moreover, we found no differences among postoperative results of the two TKA designs.
Conclusion
Despite design variations, no difference has been found among the prostheses in terms of PROM, rotations and translations. Both design kinematics did not show paradoxical external rotations, but an increase in femoral translation in mid-flexion without affecting the functioning of the prosthesis.
Level of evidence
II.
We analyze a model that accounts for the inherently large thermal lattice fluctuations associated with the weak van der Waals intermolecular bonding in crystalline organic semiconductors. In these ...materials the charge mobility generally exhibits a "metalliclike" power-law behavior, with no sign of thermally activated hopping characteristic of carrier self-localization, despite apparent mean free paths comparable to or lower than the intermolecular spacing. Our results show that such a puzzling transport regime can be understood from the simultaneous presence of band carriers and incoherent states that are dynamically localized by the thermal lattice disorder.
We study the spectral properties of a system of electrons interacting through long-range Coulomb potential on a one-dimensional chain. When the interactions dominate over the electronic bandwidth, ...the charges arrange in an ordered configuration that minimizes the electrostatic energy, forming Hubbard's generalized Wigner lattice. In such strong-coupling limit, the low-energy excitations are quantum domain walls that behave as fractionalized charges and can be bound in excitonic pairs. Neglecting higher-order excitations, the system properties are well described by an effective Hamiltonian in the subspace with one pair of domain walls, which can be solved exactly. The optical conductivity σ(ω) and the spectral function A(k,ω) can be calculated analytically and reveal unique features of the unscreened Coulomb interactions that can be directly observed in experiments.
We provide a phenomenological formula that describes the low-frequency optical absorption of charge carriers in disordered systems with localization. This allows us to extract, from experimental data ...on the optical conductivity, the relevant microscopic parameters determining the transport properties, such as the carrier localization length and the elastic and inelastic scattering times. This general formula is tested and applied here to organic semiconductors, where dynamical molecular disorder is known to play a key role in the transport properties. The present treatment captures the basic ideas underlying the recently proposed transient localization scenario for charge transport, extending it from the dc mobility to the frequency domain. When applied to existing optical measurements in rubrene fieldeffect transistors, our analysis provides quantitative evidence for the transient localization phenomenon. Possible applications to other disordered electronic systems are briefly discussed.
Electron spin relaxation rate (eSR) is investigated on several organic semiconductors of different morphologies and molecular structures, using avoided level crossing muon spectroscopy as a local ...spin probe. We find that two functionalized acenes (polycrystalline tri(isopropyl)silyl-pentacene and amorphous 5,6,11,12-tetraphenyltetracene) exhibit eSRs with an Arrhenius-like temperature dependence, each with two characteristic energy scales similar to those expected from vibrations. Polycrystalline tris(8-hydroxyquinolate)gallium shows a similar behavior. The observed eSR for these molecules is no greater than 0.85 MHz at 300 K. The variety of crystal structures and transport regimes that these molecules possess, as well as the local nature of the probe, strongly suggest an intramolecular phenomenon general to many organic semiconductors, in contrast to the commonly assumed spin relaxation models based on intermolecular charge-carrier transport.
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